NASA's Curiosity Finds Surprise Clues to Mars' Watery Past

Among other discoveries made by the rover, rippled rock textures suggest lakes existed in a region of ancient Mars that scientists expected to be drier.

So Curiosity’s team was surprised to discover the mission’s clearest evidence yet of ancient water ripples that formed within lakes.

Billions of years ago, waves on the surface of a shallow lake stirred up sediment at the lake bottom, over time creating rippled textures left in rock.

https://mars.nasa.gov/news/9344/nasas-curiosity-finds-surprise-clues-to-mars-watery-past/